PO-446 Anti-tumour efficiency of 20A, a novel G-quadruplex ligand, in in vitro and in vivocancer models: ATM and autophagy interplay

Introduction G-quadruplexes are non-canonical DNA structures that can be stabilised by molecules called G-quadruplex ligands (G4L). G4L were first found to target telomeres and inhibit telomerase activity in cancer cells, limiting cell proliferation and making them attractive for cancer therapy. However, it has been proposed that some G4L can exert anti-tumour properties through telomerase-independent mechanisms. In this line, we investigated the underlying molecular mechanisms and anti-tumour effects of a novel G4L (20A) in several cancer models. Material and methods We assessed the in vitro anti-proliferative capacity of 20A in cervical carcinoma (HeLa), lung adenocarcinoma (A549), and osteosarcoma (Saos-2) cell lines by measuring cell viability, senescence and apoptosis. We used two in vivo cancer models: HeLa-cell subcutaneous and A549-cell lung orthotopic xenograft mouse models. Mice were treated by peri-tumoral and intraperitoneal 20A injections, respectively. Activation of the DNA Damage Response (DDR) and autophagy pathways were assessed by western blot analysis of the DDR kinase ATM phosphorylation and the autophagic marker LC3-II accumulation, respectively. Targeted genetic depletion of ATM and autophagic genes (ATG5 and ATG7) allowed analysing their role in 20A cytotoxicity. Results and discussions We found that 20A treatment causes a significant and rapid cell growth inhibition in three different types of cancer cell lines. This effect is associated with senescence induction and apoptosis through a p53-independent mechanism. Moreover, we show that 20A significantly reduces tumour growth in both in vivo cancer models used. To gain further insight into the molecular mechanisms involved in 20A cytotoxicity, we performed transcriptomic analysis which revealed functional enrichment in DDR and autophagy pathways upon 20A treatment. We confirmed these data by western blot and found that ATM is required for 20A-induced autophagy. Finally, disruption of both DDR and autophagy compromised senescence onset and increased apoptosis. Conclusion In this study, we revealed the anti-tumour properties of this new G4L 20A in diverse in vitro and in vivo cancer models. We also show that targeting the ATM/autophagy pathway could potentiate 20A therapeutic efficiency. To our knowledge, this is the first evidence of the pivotal role of the ATM/autophagy axis in the decision between senescence and apoptosis in response to a G4L.Together, our data support further studies about 20A as a potential anti-cancer drug.